Bovine Spongiform Encephalopathy

Last Modified: May 23, 2025
Black cow with white face next to three all-black calves.

Bovine spongiform encephalopathy (BSE), widely referred to as “mad cow disease,” is a progressive and fatal disease of the nervous system in cattle. It results from infection by a "prion," an abnormal cellular protein found mostly in the brain. BSE is not contagious. Cattle become infected by eating prion-contaminated feed.

BSE is rare, occurring at a rate of less than one case per million cattle worldwide. However, it's a reportable animal disease. It also presents a public health concern because of its link to cases of variant Creutzfeldt-Jakob disease in people.

The World Organisation for Animal Health classifies the United States as "negligible risk" for BSE. This is based on our country’s history with the disease (only seven cases from 2003 to 2023), control measures in place, and robust BSE surveillance system.

Cattle affected by BSE experience progressive degeneration of the nervous system. Signs usually don't appear until about 3–6 years after initial infection.

Here's what to look for:

  • Changes in temperament (nervousness or aggression)
  • Abnormal posture
  • Coordination problems and difficulty in rising
  • Weight loss
  • Decreased milk production
  • Loss of condition without noticeable loss of appetite

After signs appear, the animal’s condition deteriorates until it dies. This usually takes anywhere from 2 weeks to 6 months.

Report Signs of Animal Disease

Producers or owners who suspect an animal disease should contact their veterinarian to evaluate the animal or herd. Find an accredited veterinarian.

Animal health professionals (veterinarians; diagnostic laboratories; public health, zoo, or wildlife personnel; and others) report diagnosed or suspected cases of nationally listed reportable animal diseases to APHIS Area Veterinarians in Charge and to the State animal health official as applicable under State reporting regulations. 

Controlling Bovine Spongiform Encephalopathy